Diabetic retinopathy is a significant complication of diabetes mellitus, one that is the leading cause of blindness in the United States. Since its clinical introduction in 1970, vitreous fluorophotometry (VFP) has been used as a sensitive, quantitative method of documenting alterations in the blood-ocular barriers. VFP has gained in importance since the accumulation of fluorescein in the vitreous has been suggested to the earliest evidence of blood-ocular barrier breakdown and may be present in all diabetics. Every VFP study conducted in diabetic animals or man that has measured fluorescein levels in the anterior chamber has shown elevated readings. These values decrease as blood-glucose levels are brought under control. No study yet reported has shown normal anterior chamber values and abnormal vitreal fluorescence. In this proposal we outline a method of evaluating the contribution of anterior segment fluorescein to vitreal measurements. If it can be demonstrated that the posterior segment is significantly influenced by anterior segment fluorescein, future research may emphasize the unadulterated readings taken in the anterior chamber. At the very least researchers would have to reconsider the "purity" of posterior segment fluorometric values. Using an appropriate animal model (minipig) sodium fluorescein will be introduced into only the anterior chamber by iontophoresis, thus allowing the study of retrograde ion movement. In another experiment, the relative contribution of anterior and posterior fluorescein will be studied by impairing either the blood-aqueous barrier or the blood-retinal barrier with a laser beam. Understanding the contribution of aqueous fluorescein to fluorophotometry values taken in the vitreous is of fundamental importance to both basic and clinical applications of VFP.